There are more than 20 million chemicals in the literature, with new materials being synthesized each week. Most of these molecules are stable, and the 3-dimensional arrangement of the atoms in the molecules, in the various solids may be determined by routine x-ray crystallography. When this is done, it is found that this vast range of molecules, with varying sizes and shapes can be accommodated by only a handful of solid structures. This limited number of architectures for the packing of molecules of all shapes and sizes, to maximize attractive intermolecular forces and minimizing repulsive intermolecular forces, allows us to develop simple models of what holds the molecules together in the solid. In this volume we look at the origin of the molecular architecture of crystals; a topic that is becoming increasingly important and is often termed, crystal engineering. Such studies are a means of predicting crystal structures, and of designing crystals with particular properties by manipulating the structure and interaction of large molecules. That is, creating new crystal architectures with desired physical characteristics in which the molecules pack together in particular architectures; a subject of particular interest to the pharmaceutical industry.

About the Author(s)

Jeffrey Huw Williams, formerly at Bureau International des Poids et Mesures (BIPM)My career has been in the physical sciences after obtaining a Ph.D. in chemical physics from Cambridge University, 1981. Firstly, as a research scientist in the universities of Cambridge, Oxford, Harvard and Illinois, and subsequently as a physicist at the Institute Laue-Langevin, France; the world's largest facility for the investigation of condensed matter science via the technique of neutron scattering. During this period as a research scientist, I published more than sixty technical papers and invited review articles in the peer-reviewed literature. I left research in 1992 and moved to the world of science publishing and the communication of science by becoming the European editor for the physical sciences for the AAAS's Science. Subsequently, I was the Assistant Executive Secretary of the International Union of Pure and Applied Chemistry, the agency responsible for the advancement of chemistry through international collaboration.

Most recently, 2003-2008, I was the head of publications at the Bureau international des poids et mesures (BIPM). The BIPM is charged by the Metre Convention of 1875 with ensuring world-wide uniformity of measurements and their traceability to the International System of Units (SI). It was during these years at the BIPM that I became interested in, and familiar with the origin of the Metric System, its subsequent evolution into the SI, and the coming transformation into the Quantum-SI.

At the BIPM, I was the editor of their journal Metrologia, the leading technical publication for research on all matters related to weights and measures (published by the IOP on behalf of the BIPM). I was also responsible for editing the English and French texts (the French being the official text) of all the BIPM's publication; this included the SI Brochure, the BIPM's flagship publication about the SI, which is written by the BIPM's Consultative Committee on Units.

Apart from my technical publications and my editorial experience at peer-review journals and magazines, I have written widely about science, technology, the impact of science on society and the individual for general-interest magazines such as New Scientist and for more specialized magazines (Chemistry in Britain, Physics Today, Chemical & Engineering News, Physics World and Chemistry and Industry).